Several animals hibernate, or become inactive in a cold climate—when animals become inactive in a hot climate, it is called estivation (see below). It is interesting to note, too, that hibernation in reptiles (such as the garter snake below) is called brumation, and differs from hibernation in mammals (like the alpine marmots below) because the reptile is not living off its fat reserves like mammals. The following lists some interesting examples of hibernators: